The maximum power available to a peripheral subsystem connected to a computer system such as, for example, a disk drive subsystem connected through a Universal Serial Bus (USB) connection to a personal computer (PC), may be a significant factor in the design of the peripheral subsystem.
A USB host device such as, for example, a laptop, notebook, netbook or desktop personal computer (PC); a personal digital assistant (PDA), a cellphone, or other intelligent device interfaces to a USB peripheral subsystem through a host controller and host driver software. The USB host controller communicates with the USB device controller in the USB peripheral subsystem over a multi-wire connection that includes power, ground, and data signals.
For example, a USB-powered disk drive subsystem, including controller and disk drive, may be limited to draw no more than a specified maximum amount of supply current over the USB connection (e.g., 500 or 900 milliamps to comply with the USB 2.0 and 3.0 Specifications, respectively). This limited amount of supply current includes that needed by the peripheral subsystem components used to interface between the USB connection and the electrical signaling standard used by, for example, a disk drive such as a Serial ATA (SATA) compatible hard disk drive or other device in the peripheral subsystem, as well as the power needed for the disk drive itself.
While a USB-connected peripheral subsystem, or other external device (e.g., a USB hub) can supply the operating power needed, doing so requires that such external devices include the necessary power supply circuitry, increasing the cost, complexity, and weight born by a the user.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of ordinary skill in the art through comparison of such systems with the present invention as set forth in the remainder of the present application with reference to the drawings.